Removal of radioactive strontium and cesium from milk



United States Patent 6 Claims. 201. 99-60) This invention relates to a process of removing strontium from milk and particularly the radioactive isotopes of strontium, as well as cesium when it is present.

It is now recognized that radioactive strontium in milk constitutes a health hazard, particularly when it is present in abnormal quantities. The problem is an increasingly important one.

The object of the present invention is to provide a process whereby milk may be treated to remove undesired strontium and cesium from milk without altering the natural flavour or composition of the milk.

In accordance with the process of the present invention, milk containing radioactive strontium is treated with a cation exchange resin substantially saturated with calcium, potassium and sodium ions to cause the radioactive strontium and cesium to be adsorbed by the resin without changing the flavour or composition of uncontaminated milk. A normal ion exchange resin, such as that known as Dowex 50W, is rendered effective in the process by treating it with an aqueous solution of salts of calcium, potassium and sodium, for example chlorides, to substantially saturate the resin with the three ions, calcium, potassium and sodium. The resin is then washed free from the chlorides. This constitutes the modified ion exchange resin used in the process.

The milk may be agitated with the so modified resin or it may be passed through a bed or column of the resin to insure removal of the radioactive elements, strontium and cesium, to the desired level. The normal ratio of calcium, potassium and sodium in milk is substantially 1:1.33:0.42 by weight. This ratio varies within about plus or minus 10% in milk supplied by city dairies. When calcium, potassium and sodium ions are incorporated in the resin in this ratio, the tendency to change the normal proportion and content of calcium, potassium and sodium in the milk is avoided. This also avoids tendency to change in the taste of the milk by the alteration of the cation composition of the milk.

In carrying out the process normal milk containing radioactive strontium and cesium was treated With the modified ion exchange resins as above described. It has been found that neither the concentration of the radioactive elements in the milk nor their source has any effect upon the efiiciency of the process in their removal by the resin. Removal of the undesired elements is most rapid on initial contact with the resin. Contact in either batch or column treatment is continued until the desired amount of the radioactive material is adsorbed by the resin. In batch operation for treatment of relatively small quantities of milk the treatment may be conveniently repeated with fresh or regenerated resin. The used resin is regenerated by washing with water and treating with solution of the chlorides of calcium, potassium and sodium to remove the radioactive ions. The so treated resin is Washed with water to remove the chlorides.

The amount of resin to be employed in a given case depends upon the volume of milk to be treated and the amount of radioactive material to be removed.

The following example is illustrative:

The modified ion exchange resin used had a practical size of plus 50 and minus (Tyler standard).

100 parts of contaminated milk were agitated with 1 part by weight of the resin for 2.5 minutes and removed in excess of 58% of the radioactive strontium and cesium present in the milk. Two such treatments removed in excess of 92%. As previously stated, the major portion of the radioactive elements are removed by the first treatment with the resin. The number of treatments used is determined by the extent to which the radioactive elements are to be removed and the volume of the resin employed to provide the resin surface contact with the milk. It will be recognized that the relative amount of resin to milk may be varied widely, since the adsorption of the radioactive strontium and cesium is achieved as a result of the surface contact where the ion exchange takes place.

In column treatment of the contaminated milk with the modified resins, one column may be used for the passage of the milk until the resin requires regeneration with a second column to be used while the resin in the first column is being regenerated. The dimensions of the column, filled with the resin, are selected in accordance with the volume of milk to be treated and the efficiency of removal of the radioactive elements required in any given case. This will be apparent to those skilled in the art of ion exchange.

What is claimed is:

1. A process for removing radioactive strontium and cesium from milk which comprises treating the milk in contact with an ion exchange resin substantially saturated with calcium, potassium and sodium ions substantially in the proportions in which said ions are present in said milk to cause the radioactive elements to be adsorbed by the resin and separating the resin from the milk.

2. The process defined in claim 1 wherein the milk and resin are agitated together to hasten the adsorption.

3. The process defined in claim 1 wherein the milk is passed through a column of the resin.

4. The prow ss defined in claim 1 wherein the treatment is repeated with a fresh batch of resin.

5. The process as defined in claim 1 wherein the resin contains calcium, potassium and sodium ions in the weight ratio of 1:1.33:O.42

6. The process of removing radioactive strontium and cesium from milk which comprises agitating the milk with an ion exchange resin substantially saturated with calcium, potassium and sodium in the relative proportions of 1:1.33:0.42 to cause adsorption of the radioactive elements by the resin and separating the resin from the milk.

References Cited by the Examiner UNITED STATES PATENTS 4/44 Hull 99-60 5/57 Loo 99-60 OTHER REFERENCES A. LOUIS MONACELL, Primary Examiner.

TOBIAS E. LEVOW, ABRAHAM H. WINKELSTEIN,

Examiners. 

1. A PROCESS FOR REMOVING RADIOACTIVE STRONTIUM AND CESIUM FROM MILK WHICH COMPRISES TREATING THE MILK IN CONTACT WITH AN ION EXCHANGE RESIN SUBSTANTIALLY SATURATED WITH CALCIUM, POTASSIUM AND SODIUM IONS SUBSTANTIALLY IN THE PROPORTIONS IN WHICH SAID IONS ARE PRESENT IN SAID MILK TO CAUSE THE RADIOACTIVE ELEMENTS TO BE ADSORBED BY THE RESIN AND SEPARATING THE RESIN FROM THE MILK. 